Improve custom-menus docs (nushell#832)

Author: CarrotManMatt

custom-menus/README.md

@@ -1,9 +1,9 @@
-# Custom menus folder 
+# Custom Menus Folder 
 
 In this folder you can find custom menus for nushell. 
 
 To make them work:
 1. insert the code of chosen menu into the `menus` section of the `config.nu` file. 
-2. Check, that the name of the menu is uniqe
+2. Check, that the name of the menu is unique
 3. Add a shortcut to call for the needed menu in the `keybindings` section of the `config.nu` file